Add, rearrange, duplicate, and delete slides in PowerPoint

Add slides

Select the slide you want your new slide to follow.
Select Home > New Slide.
Select a layout.
Select the text box and type.

Delete slides

For a single slide: Right-click and select Delete Slide.
For multiple slides: Hold Ctrl and select the slides. Then right-click and select Delete Slide.
For a sequence of slides: Hold Shift and select the sequence. Then right-click and select Delete Slide.

Source: Microsoft